trying to pull down (aka GET) all files with extension BAK for all subfolders under a specific root folder

A general "get " pulls down all files in all subfolders, even keeping the same folder structure, which is great. But I cannot restrict it to just pulling down BAK files with a "get .bak" command
I get "Globing pattern didn't match any file"

This is a Windows system (2008) and Tectia 6.4.8.305
What am I missing?

So if I understand correctly you want to basically filter and only transfer .bak files while preserving the directory structure. I don't believe this is possible to do with sftpg3 as when you use a globing pattern sftpg3 will try to match the pattern also to the subdirectories.